Networks are based on architectures which may be under development. 3GPP is one group which develops networks worldwide and provides standards for communication networks and devices within the networks.
In the current standardization activities of 3GPP there is a work ongoing in the working group SA2 WG for Support of Local IP access (LIPA) for the Home (e)NodeB Subsystem and of Selected IP traffic offload (SIPTO) for the Home (e)NodeB Subsystem and for the macro layer network may be required in TS 22.220 and TS 22.101.
The working group is specifying the TR 23.829 for LIPA and SIPTO and there the downlink paging support for LIPA may be currently an open issue to be solved in the so called “solution proposals 1 and 2”.
The current LIPA/SIPTO Architecture comprising different embodiments, i.e. “solution proposals 1 and 6” in the standardization document TR 23.829 may necessitate termination of an additional core network interface to the (H)eNB collocated L-GW for LIPA Bearer Service management.
This core network interface may be S11-like interface from MME to the (H)eNB/L-GW in the variant where L-GW is modeled as a local S-GW/P-GW, or S5-like interface when L-GW is modeled as a local P-GW.
The “solution proposal 6” may assume specifying a new “extension tunnel” from P-GW to the (H)eNB/L-GW.
“Solution proposal 2” in the TR 23.829 may assume that the L-GW function for LIPA service will not have any additional control interface to the already existing S1-MME between EUTRAN and EPC (Core Network).
The ordinary paging trigger upon arriving downlink packet to the S-GW may not be applied as LIPA traffic does not traverse via the Core Network nodes. Thus some further mechanism may be needed for initiating the UE paging with LIPA services.
It may be foreseen in relation to solution 2 that “downlink paging support for LIPA requires special mechanism that may be problematic, e.g. tunnel traffic over Internet to PGW/GGSN”. This is because the PGW/GGSN may not be reachable via the Internet (could be behind a NAT function or a Firewall).
Further proposals may use only the S1-MME interface for all LIPA control. Again here the “downlink paging support for LIPA can be considered open issue as it would need changes to the S1AP protocol in 3GPP.
It may also be foreseen a LIPA/SIPTO architecture where the L-GW is implemented with Core Network GWs (S-GW and P-GW) that are just moved close to (H)eNB or collocated with (H)eNB. In this case the standard procedures for paging can be used as the S-GW behaves as paging agent and has S11 (or L-S11) interface to the MME for triggering paging as usual.
However, this kind of a solution may be not suitable for simple LIPA access from HeNBs, since it may break the clear RAN—Core split and would necessitate storing sensitive User Context e.g. IMSI in the HeNB/L-GW node installed to customer premises (untrusted from MNO point of view) etc.
There may be further approaches for supporting more optimized paging trigger from (H)eNB/L-GW to the MME.
In the content of WO2008/132163 there may be assumed that (H)eNB/L-GW has a local Paging Agent that can generate a paging command message and send it locally to all (H)eNBs in the Tracking Area providing LIPA (Local Breakout) Service. This method has a disadvantage that it requires the local Paging Agent to emulate MME in the EPC as the originator of the paging command in order to avoid changes in the UEs.
Moreover, further solutions in relation to paging and managed remote access in Local IP breakout may assume that the (H)eNB collocated L-GW has a S5-like interface to the S-GW placed in the EPC through which the L-GW sends uplink data packet that further triggers paging in the S-GW and MME as usual. This method has a disadvantage that an additional core network interface must be terminated in EUTRAN node and the L-GW should implement 3GPP proprietary P-GW functions for simple IP traffic bridging between local network and data radio bearer in (H)eNB.
In addition, further solutions in relation to optimized interface for Local IP Access may assume that only S1-MME interface will be needed for controlling LIPA feature in HeNB collocated L-GW that implements a local Paging Agent function that sends a new control message to the MME over S1-MME interface to trigger UE paging via MME. This method has disadvantage that upon UE movement to the Idle-mode the UE specific S1AP connection is released so a common S1AP elementary procedure from (H)eNB to MME should be used.
There may be a need for a solution for a downlink paging support for LIPA services.